OP, as others have said, reconstructing a PvP encounter without video is inherently speculative, but nevertheless based upon your brief account, here is my speculation as to what happened:
1. From the moment the interdiction completed, the FAS began an all-out high-alpha attack upon you, probably using plasma and quite possibly ramming.
2. At some point within this assault you were hit by one of three weapons: (a) a Yuri Grom FSD disruptor missile; (b) a standard dumdbfire missile modded with the FSD disruption effect; or (c) a mine modded with the shift-lock effect; all three of which cause your FSD to reboot.
3. The reason why your weapons would not deploy is because your powerplant malfunctioned and all your weapons are set at higher than 40% power requirement. Your powerplant malfunction may have been caused indirectly (by scramble spectrum and bad luck on the RNG of which module was affected) or directly (by damage). My personal expectation is that from the outset your attacker had your powerplant targeted and after your shield dropped you simply took three balls of plasma straight into it, causing a malfunction, before subsequent volleys killed you.
There is no absolute defence against the FSD disruption effects in an Anaconda, if the attacker is competent and fires the missiles/mines at close range. The main issue is range control (too close and mines will hit you, too far and reverberating cascade torpedoes, if present, will detonate.) As, however, the FSD disruption is followed by a long cooldown, it merely enlarges the window of time you have to survive in.
The way to survive this encounter was to have a very strong engineered shield array fitted, keep 4 pips in sys, boost away from your attacker and turn with FA-off, check his loadout and control range depending on what he has, and wait out the FSD cooldown and any disruption. Not necessarily easy but not as difficult as it may sound.
